1. Field of the Invention
The present invention relates to a method for direct smelting reduction of Ni ore in a smelting reduction furnace by the use of carbonaceous material as a fuel or a reducing material.
2. Description of the Prior Arts
Materials such as scrap, ferro alloy, electrolytic Ni or the like have previously been used in melting and refining in a process of manufacturing stainless steel. Those materials are melted in an electric furnace or a converter. Cr and Ni being major components of stainless steel in the state of ferrochrome and ferronickel are charged into the electric furnace or the converter. Chromium ore and nickel ore are required to be previously reduced in the electric furnace or the like to manufacture ferrochrome and ferronickel. Expensive electric energy is used for reducing chromium ore and nickel ore. Accordingly, a method wherein ferrochrome and ferronickel are used as materials is not an economical method. In terms of the above-described circumstances, there has been proposed a method wherein Cr ore is used as a source of Cr to economically manufacture stainless steel and the Cr ore is smelted and reduced in a converter or another other smelting furnace.
On the other hand, four methods, which will be described as follows, are pointed out as methods of using inexpensive material for a source of Ni. A first method is a method wherein molten metal of FeNi is directly used in an electric furnace for a purpose of reducing a cost of melting FeNi. This method is described in the magazine "Iron and Steel" [69 (1983) 7, p.59]. A second method is a method for smelting and reducing Nickel matte in a converter which is disclosed in a Japanese Patent Publication Laid Open No. 104153/83. A third method is disclosed in a Japanese Patent Publication Laid Open No. 36613/85. In this method, material produced by mixing nickel oxide with carbonaceous material and forming a mixture thus obtained is heated and prereduced and the material prereduced is charged into a converter type reaction vessel, in which it is smelted and reduced. A fourth method is a method wherein nickel oxide is used ( Japanese Patent Publication Laid Open No. 291911/86).
In the above-mentioned citations, however, Ni ore is not directly smelted and reduced in a smelting furnace. Since Ni ore has a low content of the 2 to 3% Ni and 80% of weight of Ni ore converts to slag, a great amount of slag is produced in a smelting reduction of the Ni ore. Accordingly, in the case where molten metal having a predetermined concentration of Ni is tried a great amount of slag is produced. In the case of obtaining molten metal containing 8 wt. % Ni, for example, 2 to 3 tons of slag per ton of molten metal are produced. In connection with the production of a great amount of slag, the following problems become remarkable.
(1) Slopping is liable to be produced by a reaction of oxygen with carbonaceous material charged into the smelting reduction furnace as a reducing material or as a heat source at the step of the smelting reduction. In consequence, a stable operation becomes difficult whereby the operation becomes unstable.
(2) Equipment is greatly damaged by the slopping; and
(3) The yield of Ni is decreased by the slopping.
In view of the foregoing problems, in the foregoing citations, Ni ore as a source of Ni is not directly charged into the smelting reduction furnace, but material having a content of Ni, whose percentage in the material is increased by subjecting the material to some preliminary treatment, is used.